Wireless relay station for radio frequency-based tracking system

ABSTRACT

System and methods of tracking a position of a mobile device with an electromagnetic signal-transmitting antenna include receiving electromagnetic signals from the transmitting antenna of the mobile device by a plurality of receiver antennae of a base station and by one or more receiver antennae of a relay station. The relay station transmits to the base station timing information associated with the electromagnetic signals received by the one or more receiver antennae of the relay station. The base station computes a position of the transmitting antenna of the mobile device based on timing information computed from the electromagnetic signals received by the plurality of receiver antennae of the base station and on the timing information received from the relay station.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 15/961,274, filed Apr. 24, 2018, titled “Wireless Relay Station for Radio Frequency-Based Tracking System,” which is a divisional of patented U.S. patent application Ser. No. 15/291,364, filed Oct. 12, 2016, titled “Wireless Relay Station for Radio Frequency-Based Tracking System,” U.S. Pat. No. 9,961,503, issued May 1, 2018, which is a continuation of patented U.S. patent application Ser. No. 14/597,360, filed Jan. 15, 2015, titled “Wireless Relay Station for Radio Frequency-Based Tracking System”, U.S. Pat. No. 9,497,728, issued Nov. 15, 2016, which claims the benefit of and priority to U.S. provisional application No. 61/928,496, filed Jan. 17, 2014, titled “Wireless Relay Station for Radio Frequency-Based Tracking System,” the entireties of which applications are incorporated by reference herein.

FIELD OF THE INVENTION

The invention relates generally to systems and methods for tracking the position of electromagnetic signal transmitting devices. In particular, the invention relates to radio frequency (RF)-based wireless position tracking systems that use one or more wireless relay stations.

BACKGROUND

Position tracking systems can use a variety of configurations for tracking the two- or three-dimensional position of a wireless device. In many arrangements, a system may require three or more base receivers (or three or more base antennae connected to a single base receiver) to receive some form of data from a wireless device and use that data to calculate the position of the device. The data can be timing information, signal strength, or angle of arrival measurements of the signal transmitted by the device and received at the base receiver(s) antennae of the system. In all arrangements, the position of the base receiver antennae of the system is important for calculating the position of the device and often these antennae are wired to the system for computing the position of the device.

Over the years, several different forms of tracking systems have evolved with the most notable being Global Positioning System or GPS. For GPS, the mobile receiver uses timing information sent from satellites and then calculates the position of the GPS receiver with the mobile receiver doing the position computation using the timing information from the satellite signals.

SUMMARY

All examples and features mentioned below can be combined in any technically feasible way.

Embodiments of position-tracking systems described herein, unlike GPS, perform position calculation using signals sent from the wireless device being tracked. This allows the device to be simple, but does add some complexity to the position-tracking system. The position-tracking systems use one or more wireless relay stations communicating with a base station which uses multiple receive locations of the wireless relay stations as coordinate references for performing timing and positioning calculations on a wireless device communicating with the base station and the wireless relay stations. By incorporating one or more wireless relay stations, the system can improve setup options, improve accuracy and provide a larger working volume for the wireless device.

One example design for a position-tracking system for three-dimensional tracking comprises at least four base receivers (or one base receiver with four base antennae) wired to the base station. These base receivers receive the wireless signals sent from the mobile wireless device being tracked and send that information to the base station for position computation. In one embodiment, the base receivers are fixed in position in space and wired to the base station. However, this design can be limiting as the wired base receivers can reduce the working volume and increase cost because they are tethered to the base station, making spacing of their antennae more difficult and expensive to setup. For example, a wireless mouse tracked in three dimensions for interaction with games or other interactive software programs can only be tracked within the working area defined by the spacing of the base receivers of the base station. If these base receivers or receiver antennae are placed around a television, the working volume is defined by the position of the base receivers, and accuracy may diminish as the device being tracked moves away from the central point of the positions of the base receivers. If the position-tracking system uses a device signal of arrival time differential compared at each receiver (or antenna) for making position calculations, this limited base receiver or receiver antenna spacing caused by a wired connection can be especially limiting.

A position-tracking system that incorporates one or more wireless relay stations to add additional measurements used for tracking by the position-tracking system can significantly improve over position-tracking systems requiring fully wired or tethered base receivers together with their corresponding antennae. Receiving timing information from the device being tracked, each relay station can expand the working volume or tracked area of the device and provide more options for product integration and position-tracking system set up. Also, by expanding the distances between total receivers or receiver antennae, the position-tracking system can improve position accuracy, allowing more precise measurements.

Each relay station communicates wirelessly with both the device being tracked and a base station performing the position tracking function. Alternatively, one or more relay stations can be wired to the base station, with wires replacing the wireless communication channel. In that embodiment, each relay station is in a fixed position, such as plugged into an electrical outlet, or be battery powered. During installation, each transmitter of each relay station acts like one or more “devices” communicating with the base station, and the base station determines the position of that transmitter. This information locates the relay station with respect to the receiver antennae of the base station. The base station also locates the position of each receiver antenna of a relay station with respect to the transmitter antennae of that relay station. Alternatively, relay stations can be placed at fixed known positions to provide the base station with the known coordinates for making position calculations.

During normal (tracking) operation, the device being tracked transmits the signal used to generate timing information, this signal being received at both the wired base antennae connected to the base station and the wireless relay station(s) receiving antenna(e). The relay station can be equipped with at least two receivers or receiver antennae and uses the multiple receive points provided by these separate receivers or antennae to compare timing differences in the device signal arrival at each receiver or receiver antenna. As the signal is received at the relay station, the time difference of arrival (or, equivalently, the phase difference of arrival) is calculated between both (or more) receivers or receiver antennae in the relay station. Because phase (θ) and time (t) are related by θ=ωt, where ω is a scalar, phase and time are equivalent systems and subsequent descriptions may be denoted by time or time differences, as appropriate.

This timing data calculated by the relay station is sent to the base station, preferably in a wireless manner, where the base station can use that timing data from each relay station receiver or receiver antenna as additional equations for calculating the position of the device. By doing timing comparisons and calculations at the relay station, the position-tracking system can avoid a timing path error from the relay station to the base station, thereby allowing the relay station to send data that is unaffected by radio propagation and interference instability, such as multipath on the round trip. Because interference like multipath is additive, removing one of the paths for this timing data significantly improves system performance through the reduction of multipath effects. If the relay station is configured with a single transceiver and antenna, techniques can reduce the effects of interference, such as implementing a duplex system whereby the receiver portion of the relay station transceiver receives at one spectrum, for example, 2.4 GHz, and the return transmission from the same relay station is at a different spectrum, for example, 5.8 GHz.

Whereas using the same antenna for both receiving and transmitting is optimal, it may not be trivial or cost effective to multiplex the circuitry attached to this antenna to achieve both functions in a real-time manner. Another technique is to place the receiver and transmitter antenna concentrically, so that they share the same origin. Designs for concentric antenna, however, may be difficult to implement.

In one embodiment, the relay station is equipped with at least two receivers, or receiver antennae, and uses two transmitters to retransmit the phase information of the device, properly coded and correlated to its signal arrival at the relay station receivers or receiver antennae. The relay station sends this phase/timing information to the position-tracking system using any of a variety of means. This transmission can be accomplished directly with common or additional wireless signal channels. These signal channels can communicate wirelessly on a different frequency channel, for example, by using different encoding. This transmission can also be sent using powerline communication. Preferably, the transmission is sent at a compatible frequency over one or both transmitter channels employed by the transmitter(s) of the relay station.

In one aspect, a method of tracking a position of a mobile device with an electromagnetic signal-transmitting antenna include receiving electromagnetic signals from the transmitting antenna of the mobile device by a plurality of receiver antennae of a base station and by one or more receiver antennae of a relay station. The relay station transmits to the base station timing information associated with the electromagnetic signals received by the one or more receiver antennae of the relay station. The base station computes a position of the transmitting antenna of the mobile device based on timing information computed from the electromagnetic signals received by the plurality of receiver antennae of the base station and on the timing information received from the relay station.

In another aspect, a position-tracking system comprises a base station with a processor, at least three spatially separated receiver antennae disposed at locations known to the processor of the base station. Each of the at least three receiver antennae receive electromagnetic signals transmitted by a transmitting antenna of a mobile device. The position-tracking system further comprises one or more relay stations in communication with the base station and with the transmitting antenna of the mobile device. Each relay station is disposed at a distance from the base station known to the processor of the base station. Each relay station comprises a processor, one or more receiving antennae that receive the electromagnetic signals transmitted by the transmitting antenna of the mobile device, and one or more transmitter antennae. The transmitter antennae of each relay station send timing information to the base station associated with the electromagnetic signals received by the one or more receiver antennae of the relay station. The processor of the base station uses the timing information received from the one or more relay stations and the timing information associated with the electromagnetic signals received by the at least three receiver antennae of the base station to compute the position of the transmitting antenna.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further advantages of this invention may be better understood by referring to the following description in conjunction with the accompanying drawings, in which like numerals indicate like structural elements and features in various figures. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

FIG. 1 is a block diagram of an embodiment of a position-tracking system, including a base station in communication with a relay station, for tracking the position of an electromagnetic signal transmitting device.

FIG. 2 is a diagram for illustrating position measurements based on device transmitter to base station receiver transmissions.

FIG. 3 is a diagram for illustrating position measurements based on relay station transmitter to base station receiver transmissions.

FIG. 4 is a diagram for illustrating position measurements based on device transmitter to relay station receiver transmissions.

FIG. 5 is a flow diagram detailing embodiments of modes of the relay station.

DETAILED DESCRIPTION

FIG. 1 shows an embodiment of a position-tracking system 10 comprising base station hardware (or simply base station) 12 in communication with multiple base receivers or receiver antennae 14 (herein referred to, interchangeably, as receiver, receiving antenna, or receiver antenna 14) and with one or more relay stations 16 (only one shown), for tracking the position of an electromagnetic signal (e.g., radio frequency) emitting transmitter or transmitter antenna 18 (herein referred to, interchangeably, as transmitter, transmitting antenna, or transmitter antenna 18). The transmitter antenna 18 is carried by, attached to, or embedded in a tracked object. Although only one transmitter antenna 18 is shown, the object can have more than one tracked transmitter antenna 18, to allow the orientation of the object to be calculated based on geometric principles. For example, two transmitter antennae, separated by a distance d, yield a pointer, because the two transmitter antennae form a line with known direction. Three transmitter antennae provide enough information to calculate a three-dimensional orientation.

To track the position of a single transmitter antenna 18 in three dimensions (x, y, z), one embodiment of the position-tracking system 10 has at least four receiver antennae 14. For two-dimensional position tracking, the position-tracking system 10 may have as few as three base receiver antennae 14. The base receiver antennae 14 are distinct and fixed in space, and provide a reference frame within which the transmitter antennae 18 is tracked. In this example, the base receiver antennae 14 are disposed around a monitor 20. Additional base receiver antennae can provide better coverage and more accuracy, at the expense of complexity and cost.

The configuration of the position-tracking system 10 can be reversed, with the base receiver antennae 14 being tracked and the transmitter antennae providing the reference frame. Alternatively, inertial sensors could be integrated in the object with the wireless transmitter antenna 18 being tracked to provide orientation.

The relay station 16 has two or more receivers or receiver antennae 22 (herein referred to, interchangeably, as receiver, receiving antenna, or receiver antenna 22) and two or more transmitters or transmitting antenna 24 (herein referred to, interchangeably, as transmitter, transmitter antenna, or transmitting antenna 24). The two or more receiver antennae 22 are at known distances apart from each other and from the transmitting antenna 24. The position-tracking system 10 can have multiple of such relay stations, with each additional relay station thus adding at least two additional receiver antennae 22 to the system 10. As noted above, additional receiver antennae provide better accuracy and coverage. These relay station receivers 22 provide the additional coverage for the position-tracking system 10 to minimize multipath and to increase range.

The relay station 16 is effectively a transceiver that, when acting as a receiver, provides additional information for a tracking algorithm used by the base station 12 to compute the position of the transmitter antenna 18. The signal received by the relay station 16 are processed at the relay station 16 (by the hardware portion of the relay station—not shown—that is part of the receiver) and re-transmitted to the base receiver antennae 14. This transmission can be done by cables or wirelessly. The relay station 16 can function similarly to the base station 12, whose operation is described below, to analyze a time of arrival difference at the multiple receiver antennae 22 that are part of the relay station 16.

Alternatively, the relay station 16 can operate with a single receiver antenna 22, in which case the received signal from the wireless transmitter antenna 18 being tracked can either be instantaneously re-transmitted by the relay station 16 (MIMO) to maintain a time relationship (provided the distance path between the relay station 16 and each base receiver antenna 14 is fixed and known) or converted to a different frequency to avoid frequency collision or interference. MIMO (Multiple-Input Multiple-Output) systems use more than one transmit antenna to send a signal on the same frequency to more than one receive antenna.

The relay station can be any one of a variety of mobile devices used for other functions, such as smart phones, tablets, or laptops, provided the position of the relay station 16 is known or remains fixed in space during position-tracking operation (i.e., when communicating with the base station 12 and the mobile transmitter antenna 18).

FIG. 2 shows an example of operation of the position-tracking system 10 using phase for timing comparisons. The base station 12 has a processor (not shown), such as a central processing unit or CPU, programmed to perform a position-tracking algorithm. The position-tracking algorithm is based on a best-fit of the time of flight measurements between the transmitter antenna 18 with the object and the base receiver antennae 14. An example implementation of the position-tracking algorithm is described in U.S. application Ser. No. 14/354,833, filed on Apr. 28, 2014, titled “Systems and Methods of Wireless Position Tracking,” the entirety of which application is incorporated by reference herein.

In this phase-based embodiment of the position-tracking system 10, the phase of the RF signal transmitted by the transmitter 18 is used to measure distance. A phase shift of 360° corresponds to one wavelength, and, by measuring the phase differences of the transmitter signal recorded at two base receiver antennae 14, the distance is calculated. In the following equations (Eq.1-Eq. 4), r1, r2, r3, and r4 represent distances between the positions of the base receiver antennae 14 and the position of the transmitter 18, and are represented by the phases. Receiver positions are denoted as rcvpos_(receiver number, position coordinate), and are fixed, known quantities. Position coordinate 1, 2, 3 represent x, y, z, respectively.

$\begin{matrix} {{r\; 1} = \sqrt{\left( {{rcvrpos}_{1,1} - x_{1}} \right)^{2} + \left( {{rcvrpos}_{1,2} - x_{2}} \right)^{2} + \left( {{rcvrpos}_{1,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 1} \right) \\ {{r\; 2} = \sqrt{\left( {{rcvrpos}_{2,1} - x_{1}} \right)^{2} + \left( {{rcvrpos}_{2,2} - x_{2}} \right)^{2} + \left( {{rcvrpos}_{2,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 2} \right) \\ {{r\; 3} = \sqrt{\left( {{rcvrpos}_{3,1} - x_{1}} \right)^{2} + \left( {{rcvrpos}_{3,2} - x_{2}} \right)^{2} + \left( {{rcvrpos}_{3,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 3} \right) \\ {{r\; 4} = \sqrt{\left( {{rcvrpos}_{4,1} - x_{1}} \right)^{2} + \left( {{rcvrpos}_{4,2} - x_{2}} \right)^{2} + \left( {{rcvrpos}_{4,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 4} \right) \\ {\delta_{1,2} = {{r\; 1} - {r\; 2}}} & \left( {{Eq}.\mspace{14mu} 5} \right) \\ {\delta_{1,3} = {{r\; 1} - {r\; 3}}} & \left( {{Eq}.\mspace{14mu} 6} \right) \\ {\delta_{1,4} = {{r\; 1} - {r\; 4}}} & \left( {{Eq}.\mspace{14mu} 7} \right) \end{matrix}$

The differences between the phase measurements (δ's, Eq. 5-Eq.7), which are calculated by the base station hardware, are used to solve for x1, x2 and x3, which represents the x, y, z positions of the device transmitter antenna 18, respectively. As is known in the art, this can be solved in a least squares algorithm, such as Levenberg-Marquardt or in a Kalman filter. Also known in the art is that more range measurements can be used to form an overdetermined solution, and also allows other methods to be used, such as weighted solutions, selecting a subset of equations, etc. These additional range measurements can be provided for by the relay station 16.

FIG. 3 shows an example of transmissions from the relay station 16 to the base receiver antennae 14. The relay station 16 resides at a location where the relay station can improve in tracking the transmitter 18. For example, this location may be on a wall, behind the user, on a ceiling. Before data from the relay station 16 can be used to improve performance, the position of the relay station 16 relative to the base station 12 needs to be determined. Specifically, the positions of the receiver antennae 22 of the relay station 16 need to be determined; this information can reside at the base station 12.

To determine the positions of the receiver antennae 22, the transmitters 24-1 and 24-2 are utilized in a first manner. These transmitters 24-1, 24-2 operate like transmitter antenna 18, except that the transmitters 24-1, 24-2 transmit at different frequencies from each other so that they can be differentiated from one another. The positions of the transmitters 24-1, 24-2 are computed just like that of the transmitter antenna 18. The equations to compute these positions are similar to Eq.1-Eq.7. The equations (Eq. 8-Eq. 14) for transmitter 24-1, which use ranges r5, r6, r7, and r8, are:

$\begin{matrix} {{r\; 5} = \sqrt{\left( {{rptrpos}_{5,1} - x_{1}} \right)^{2} + \left( {{rptrpos}_{5,2} - x_{2}} \right)^{2} + \left( {{rptrpos}_{5,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 8} \right) \\ {{r\; 6} = \sqrt{\left( {{rptrpos}_{6,1} - x_{1}} \right)^{2} + \left( {{rptrpos}_{6,2} - x_{2}} \right)^{2} + \left( {{rptrpos}_{6,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 9} \right) \\ {{r\; 7} = \sqrt{\left( {{rptrpos}_{7,1} - x_{1}} \right)^{2} + \left( {{rptrpos}_{7,2} - x_{2}} \right)^{2} + \left( {{rptrpos}_{7,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 10} \right) \\ {{r\; 8} = \sqrt{\left( {{rptrpos}_{8,1} - x_{1}} \right)^{2} + \left( {{rptrpos}_{8,2} - x_{2}} \right)^{2} + \left( {{rptrpos}_{8,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 11} \right) \\ {\delta_{5,6} = {{r\; 5} - {r\; 6}}} & \left( {{Eq}.\mspace{14mu} 12} \right) \\ {\delta_{5,7} = {{r\; 5} - {r\; 7}}} & \left( {{Eq}.\mspace{14mu} 13} \right) \\ {\delta_{5,8} = {{r\; 5} - {r\; 8}}} & \left( {{Eq}.\mspace{14mu} 14} \right) \end{matrix}$

And the equations (Eq. 15-Eq. 21) for transmitter 24-2, which uses ranges r9, r10, r11, and r12, are:

$\begin{matrix} {{r\; 9} = \sqrt{\left( {{rptrpos}_{9,1} - x_{1}} \right)^{2} + \left( {{rptrpos}_{9,2} - x_{2}} \right)^{2} + \left( {{rptrpos}_{9,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 15} \right) \\ {{r\; 10} = \sqrt{\left( {{rptrpos}_{10,1} - x_{1}} \right)^{2} + \left( {{rptrpos}_{10,2} - x_{2}} \right)^{2} + \left( {{rptrpos}_{10,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 16} \right) \\ {{r\; 11} = \sqrt{\left( {{rptrpos}_{11,1} - x_{1}} \right)^{2} + \left( {{rptrpos}_{11,2} - x_{2}} \right)^{2} + \left( {{rptrpos}_{11,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 17} \right) \\ {{r\; 12} = \sqrt{\left( {{rptrpos}_{12,1} - x_{1}} \right)^{2} + \left( {{rptrpos}_{12,2} - x_{2}} \right)^{2} + \left( {{rptrpos}_{12,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 18} \right) \\ {\delta_{9,10} = {{r\; 9} - {r\; 10}}} & \left( {{Eq}.\mspace{14mu} 19} \right) \\ {\delta_{9,11} = {{r\; 9} - {r\; 11}}} & \left( {{Eq}.\mspace{14mu} 20} \right) \\ {\delta_{9,12} = {{r\; 9} - {r\; 12}}} & \left( {{Eq}.\mspace{14mu} 21} \right) \end{matrix}$

These two sets of equations, (Eq. 8-Eq. 14) and (Eq. 15-Eq. 21) are used separately to solve for x1, x2 and x3, which represents the x, y, z, position, of each transmitter antenna 24-1 and 24-2, respectively.

After the positions of transmitters 24-1 and 24-2 are known, it is straightforward to determine the positions of the receiver antennae 22. The two computed locations of the transmitter antennae 24-1 and 24-2 provide reference points for determining the locations of the receiver antennae 22. Geometry and knowledge of the antennae layout provides the locations of the receiver antennae 22. An example is to place receiver antenna 22 in a line between transmitter antenna 24-1 and 24-2. This provides exact knowledge of where each receiver antenna 22 is positioned. This calculation can be performed at the relay station 16 or at the base station 12. After these positions are determined, the second means of use of transmitter antennae 24-1, 24-2 occurs. The relay station 16 transmits this position information using the same transmitter antennae 24-1, 24-2 using standard information transmission methods, such as used for cellular communication, Wi-Fi, etc., as is known in the art. Both the base station 12 and the relay station 16 contain standard circuitry for performing this operation and is multiplexed in at the appropriate setup time while the position-tracking system 10 is in a setup mode.

In one alternative embodiment, the receiver antennae 22 and transmitter antennae 24 of the relay station 16 may be embodied in a single antennae and transmission/receipt of signals can be separated by time or frequency. In another alternative embodiment, the position of the transmitter antennae 24 and receiver antennae 22 may be fixed using another device, such as a GPS or mobile phone with locating ability. For example, a user might determine the position of antennae 22 and 24 as derived from another device (GPS) and this information would be transmitted to the base station 12. Subsequently, as described above, the relay station 16 can provide tracking information for the device transmitter 18.

FIG. 4 illustrates the additional receiver paths between the transmitter antenna 18 and the relay station receiver antennae 22-1 and 22-2. Path r13 and path r14 correspond to the distances between the transmitter 18 and the receiver antennae 22-1 and 22-2, respectively. Relay station receiver positions are denoted as rptrpos_(receiver number,position coordinate), and are fixed, known quantities, as determined above in connection with FIG. 3. Position coordinates 1, 2, 3 represent x, y, z, respectively. The measurements of the two ranges r13 and r14 are performed in a similar manner to the equations used by the base station 12 to compute the position of the transmitter 18.

$\begin{matrix} {{r\; 13} = \sqrt{\left( {{rptrpos}_{13,1} - x_{1}} \right)^{2} + \left( {{rptrpos}_{13,2} - x_{2}} \right)^{2} + \left( {{rptrpos}_{13,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 22} \right) \\ {{r\; 14} = \sqrt{\left( {{rptrpos}_{14,1} - x_{1}} \right)^{2} + \left( {{rptrpos}_{14,2} - x_{2}} \right)^{2} + \left( {{rptrpos}_{14,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 23} \right) \\ {\delta_{13,14} = {{r\; 13} - {r\; 14}}} & \left( {{Eq}.\mspace{14mu} 24} \right) \end{matrix}$

The difference between the phase measurements (613, 14, Eq. 24), which is calculated in the hardware (e.g., processor) of the relay station 16 in a similar method to those determined at the base station 12, is used by the base station 12 together with Eq. 5, Eq. 6, and Eq. 7 to solve for x1, x2 and x3, which represents the x, y, z, position of the transmitter 18, respectively.

Before the base station 12 can use the computed value for 613, 14, from equation (Eq. 24), the relay station 16 needs to send the value to the base station 12. This information is transmitted using the same transmitter antennae 24-1, 24-2 using standard information transmission methods such as used for cellular communication, Wi-Fi, etc., as is known in the art. Both the base station 12 and the relay station 16 contain standard circuitry for performing this operation, which is multiplexed in at the appropriate setup time while the position-tracking system 10 is in a tracking mode.

The relay station 16 is then placed in a mode that allows its two transmitters 24-1 and 24-2 to transmit distinguishable signals and to the base receiver antennae 14. As is known in the art, this can take the form of frequency or time multiplexing. Similarly to how the transmitter antenna 18 is located using equations (Eq. 1-Eq. 7), the transmitters 24-1 and 24-2 are located using the same equations, but with ranges r5-r8 (FIG. 3) and r9-r12 (FIG. 3), respectively, substituting for ranges r1-r4. This provides an x, y, z, position of each transmitter 24-1 and 24-2. From the positions of the transmitters 24-1 and 24-2, the locations of the receiver antennae 22-1, 22-2 can be determined as described in connection with FIG. 3.

FIG. 5 is an embodiment of a process 50 illustrating operating modes of the position tracking system 10. When position tracking system 10 is started, or when commanded, it enters the selection mode 52. In the selection mode, a mode is selected either to enter normal device tracking or to set up the relay station 16. If, at step 54, normal tracking is selected, the program enters normal tracking mode 64. If instead, at step 54, the selected mode is to set up the relay station 16, the process 50 proceeds to block 56. At block 56, the transmitting antennae 24-1, 24-2 turn on such that transmitting antennae 24-1, 24-2 are transmitting on different frequencies from each, as if transmitting antennae 24-1, 24-2 were separate devices being tracked (like a device with transmitter 18).

In addition, the base station 12 is set (step 58) to track the transmitting antennae 24-1, 24-2, and, thus, to determine (step 60) their positions using equations Eq. 8-Eq. 21. The positions of the transmitting antennae 24-1, 24-2 are saved at the base station 12 so that equations Eq. 22-Eq. 24 can be utilized to improve tracking performance. At step 62, the relay station 16 switches over from generating device signatures to transmitting phase difference data produced by calculating equations Eq. 22-Eq. 24.

After step 62 completes, or if normal tracking mode has already been entered, the position-tracking system 10 starts tracking the device (i.e., the device transmitting antenna 18). This tracking is accomplished by using the base station 12 to obtain (step 66) phase difference data from signals received by the base receiver antennae 10, processed by phase differencing hardware, and computing phase differences as described by equations Eq. 5-Eq. 7. The base station 12 also has channels (which may be multiplexed from the base receiver antennae 14, or in parallel) for receiving (step 68) the digital RF encoded data that is coming from the relay station 16, which represents the phase difference (δ_(13, 14)=r13-r14) measured at the relay station 16. Equations for device position computation (for example, Eq. 1-7 and Eq. 22-24) are performed in step 70 and another computation cycle repeats, starting at step 66.

In one embodiment, a wireless relay station 16 is disclosed. The wireless relay station can be powered by battery or electrical outlet, but the encoded data connection to the base station 12 is completely wireless. In the general embodiment, a single multiplexed antenna or separate transmit and receive antennae are incorporated at the relay station. The range of each transmit antenna 24 in the relay station 16 is first determined as if it were a normal tracked device. This determines the range between the relay station 16 and the base station 12. For non-concentric transmit/receive antennae, a simple hook and appropriate weight can place the relay station 16, and, therefore, the physical antennae placement, into a known relationship. More elaborate schemes are detailed in the discussion of FIG. 3. This is all performed in a setup mode, as described previously in the process 50 described in FIG. 5.

After the locations of the relay stations transmitters 24 are determined, the range from the transmit antenna 24 of the relay station 16 to the base station antennae 14 can be converted to phase measurements 6 i and used to offset the total range from the device to the relay station and then to the base station antennae. This provides another set of equations, as illustrated in equations Eq. 25-Eq. 33.

$\begin{matrix} {{r\; 1} = \sqrt{\left( {{rcvrpos}_{1,1} - x_{1}} \right)^{2} + \left( {{rcvrpos}_{1,2} - x_{2}} \right)^{2} + \left( {{rcvrpos}_{1,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 25} \right) \\ {{r\; 2} = \sqrt{\left( {{rcvrpos}_{2,1} - x_{1}} \right)^{2} + \left( {{rcvrpos}_{2,2} - x_{2}} \right)^{2} + \left( {{rcvrpos}_{2,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 26} \right) \\ {{r\; 3} = \sqrt{\left( {{rcvrpos}_{3,1} - x_{1}} \right)^{2} + \left( {{rcvrpos}_{3,2} - x_{2}} \right)^{2} + \left( {{rcvrpos}_{3,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 27} \right) \\ {{r\; 4} = \sqrt{\left( {{rcvrpos}_{4,1} - x_{1}} \right)^{2} + \left( {{rcvrpos}_{4,2} - x_{2}} \right)^{2} + \left( {{rcvrpos}_{4,3} - x_{3}} \right)^{2}}} & \left( {{Eq}.\mspace{14mu} 28} \right) \\ {r_{relaystation} = \sqrt{\begin{matrix} {\left( {{rcvrpos}_{{relaystation},1} - x_{1}} \right)^{2} +} \\ {\left( {{rcvrpos}_{{relaystation},2} - x_{2}} \right)^{2} +} \\ \left( {{rcvrpos}_{{relaystation},3} - x_{3}} \right)^{2} \end{matrix}}} & \left( {{Eq}.\mspace{14mu} 29} \right) \\ {\delta_{1,{relaystation}} = {{r\; 1} - r_{relaystation} - \Theta_{1}}} & \left( {{Eq}.\mspace{14mu} 30} \right) \\ {\delta_{2,{relaystation}} = {{r\; 2} - r_{relaystation} - \Theta_{2}}} & \left( {{Eq}.\mspace{14mu} 31} \right) \\ {\delta_{3,{relaystation}} = {{r\; 3} - r_{relaystation} - \Theta_{3}}} & \left( {{Eq}.\mspace{14mu} 32} \right) \\ {\delta_{4,{relaystation}} = {{r\; 4} - r_{relaystation} - \Theta_{4}}} & \left( {{Eq}.\mspace{14mu} 33} \right) \end{matrix}$

Here, r1-r4 are again the equations for the base station antennae ranges to the device transmitter 18; r_(relaystation) is the range between the relay station 16 to the device transmitter 18. Additional equations Eq. 30-Eq. 33 are now available for incorporating into the tracking solution. In Eq. 30-Eq. 33, Θ_(i) corresponds to wave cycles to prevent cycle ambiguity, an example use of which is described in U.S. patent application Ser. No. 13/975,724, filed Aug. 26, 2013, and titled “Radio Frequency Communication System,” the entirety of which application is incorporated by reference herein. One way to provide phase measurement or related timing data (calculated from Eq. 30-33) to the base station 12 is for the relay station 16 to transmit it on a separate frequency. Additional circuitry at the base station 12 can provide filtering means to separate this data from direct transmission from the device transmitter 18. Other techniques such as spread spectrum encoding and decoding can be used to allow multiple devices to share limited bandwidth without interference. Ultra wideband or similar wide spectrum transmission techniques, comparing time stamped pulsed signals sent from the device transmitter to the relay and/or base station, can also determine range and therefore provide O or cycle wave count between device transmitter to the relay station and/or base station receiver antennae.

One of ordinary skill in the art will recognize that labelling the base station and the relay station is a designer choice. Further, processing of signal data (i.e., the equations above) and consolidation of the results from different receivers to track an object may be split among processors at the base and relay stations.

As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, method, and computer program product. Thus, aspects of the present invention may be embodied entirely in hardware, entirely in software (including, but not limited to, firmware, program code, resident software, microcode), or in a combination of hardware and software. All such embodiments may generally be referred to herein as a circuit, a module, or a system. In addition, aspects of the present invention may be in the form of a computer program product embodied in one or more computer readable media having computer readable program code embodied thereon.

The computer readable medium may be a computer readable storage medium, examples of which include, but are not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination thereof. As used herein, a computer readable storage medium may be any tangible medium that can contain or store a program for use by or in connection with an instruction execution system, apparatus, device, computer, computing system, computer system, or any programmable machine or device that inputs, processes, and outputs instructions, commands, or data. A non-exhaustive list of specific examples of a computer readable storage medium include an electrical connection having one or more wires, a portable computer diskette, a floppy disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), a USB flash drive, an non-volatile RAM (NVRAM or NOVRAM), an erasable programmable read-only memory (EPROM or Flash memory), a flash memory card, an electrically erasable programmable read-only memory (EEPROM), an optical fiber, a portable compact disc read-only memory (CD-ROM), a DVD-ROM, an optical storage device, a magnetic storage device, or any suitable combination thereof.

Program code may be embodied as computer-readable instructions stored on or in a computer readable storage medium as, for example, source code, object code, interpretive code, executable code, or combinations thereof. Any standard or proprietary, programming or interpretive language can be used to produce the computer-executable instructions. Examples of such languages include C, C++, Pascal, JAVA, BASIC, Smalltalk, Visual Basic, and Visual C++.

Transmission of program code embodied on a computer readable medium can occur using any appropriate medium including, but not limited to, wireless, wired, optical fiber cable, radio frequency (RF), or any suitable combination thereof.

The program code may execute entirely on a user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on a remote computer or server. Any such remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

In addition, the described methods can be implemented using ultrawideband for direct range measurement between the device and the base and relay stations, on an image processing device and/or infrared ranging at either the mobile device or at the base and/or relay stations, or the like, or on a separate programmed general purpose computer. Additionally, the methods of this invention can be implemented on a special purpose computer, a programmed microprocessor or microcontroller and peripheral integrated circuit element(s), an ASIC or other integrated circuit, a digital signal processor, a hard-wired electronic or logic circuit such as discrete element circuit, a programmable logic device such as PLD, PLA, FPGA, PAL, or the like. In general, any device capable of implementing a state machine that is in turn capable of implementing the proposed methods herein can be used to implement the image processing system according to this invention.

Furthermore, the disclosed methods may be readily implemented in software using object or object-oriented software development environments that provide portable source code that can be used on a variety of computer or workstation platforms. Alternatively, the disclosed system may be implemented partially or fully in hardware using standard logic circuits or a VLSI design. Whether software or hardware is used to implement the systems in accordance with this invention is dependent on the speed and/or efficiency requirements of the system, the particular function, and the particular software or hardware systems or microprocessor or microcomputer systems being utilized. The methods illustrated herein however can be readily implemented in hardware and/or software using any known or later developed systems or structures, devices and/or software by those of ordinary skill in the applicable art from the functional description provided herein and with a general basic knowledge of the computer and image processing arts.

Moreover, the disclosed methods may be readily implemented in software executed on programmed general purpose computer, a special purpose computer, a microprocessor, or the like. In these instances, the systems and methods of this invention can be implemented as program embedded on personal computer such as JAVA® or CGI script, as a resource residing on a server or graphics workstation, as a routine embedded in a dedicated fingerprint processing system, as a plug-in, or the like. The system can also be implemented by physically incorporating the system and method into a software and/or hardware system.

Relative terms used herein, such as top, bottom, front, back, side, left, right, above, below, upper, and lower, refer to how features of the apparatus appear in the figures, and serve to facilitate the description of the invention, and are not meant to be interpreted as limitations.

While this invention has been described in conjunction with a number of embodiments, it is evident that many alternatives, modifications and variations would be or are apparent to those of ordinary skill in the applicable arts. Accordingly, it is intended to embrace all such alternatives, modifications, equivalents, and variations that are within the spirit and scope of this invention. 

What is claimed is:
 1. A method of determining a position of a mobile device, the method comprising the steps of: sending, by a first mobile device of a plurality of mobile devices, a first wireless transmission; sending, by a second mobile device of the plurality of mobile devices, a first wireless transmission; receiving, by the first mobile device, the first wireless transmission sent by the second mobile device; sending, by the first mobile device, a second wireless transmission that conveys information about the first wireless transmission sent by the second mobile device; receiving, by a base station, the first and second wireless transmissions sent by the first mobile device and the first wireless transmission sent by the second mobile device; calculating, by the base station, a physical position of the first mobile device based on the first wireless transmission sent by the first mobile device; and calculating, by the base station, a physical position of the second mobile device based on the first wireless transmission sent by the second mobile device, the calculated physical position of the first mobile device, and the information about the first wireless transmission sent by the second mobile device that was conveyed by the second wireless transmission of the first mobile device.
 2. The method of claim 1, further comprising measuring, by the first mobile device, a phase difference based on the first wireless transmission sent by the second mobile device, and wherein the information about the first wireless transmission sent by the second mobile device that was conveyed by the second wireless transmission of the first mobile device includes the measured phase difference.
 3. The method of claim 1, further comprising measuring, by the first mobile device, a phase difference based on the first wireless transmission sent by the second mobile device, and wherein the information about the first wireless transmission sent by the second mobile device that was conveyed by the second wireless transmission of the first mobile device includes the measured time difference of arrival information.
 4. The method of claim 1, further comprising determining orientation of the second mobile device.
 5. The method of claim 1, wherein the step of calculating a physical position of the first mobile device of the plurality of mobile devices based on the first wireless transmission sent by the first mobile device includes the step of determining a physical location of each transmitting antenna of the first mobile device relative to each receiver antennae that receives the first wireless transmission of the first mobile device.
 6. The method of claim 5, wherein each transmitting antenna of the first mobile device transmits radio-frequency signals at a different frequency from each other transmitting antenna of the first mobile device.
 7. The method of claim 5, wherein the step of calculating a physical position of the first mobile device of the plurality of mobile devices based on the first wireless transmission sent by the first mobile device includes the step of determining a position of each receiver antenna of the first mobile device with respect to each transmitting antenna of the first mobile device.
 8. The method of claim 7, wherein the step of determining the position of each receiver antenna of the first mobile device with respect to each transmitting antenna of the first mobile device occurs at the first mobile device, and further comprising the step of sending by the first mobile device the position of each receiver antenna of the first mobile device in a third wireless transmission.
 9. The method of claim 7, wherein the step of determining the position of each receiver antenna of the first mobile device with respect to each transmitting antenna of the first mobile device includes the step of determining each position of that receiver antenna of the first mobile device using a global positioning system (GPS).
 10. The method of claim 1, wherein the second wireless transmission by the first mobile device that conveys the information about the first wireless transmission sent by the second mobile device occurs over a frequency channel different from a frequency channel over which the second mobile device sent the first wireless transmission.
 11. A position tracking system, comprising: a plurality of mobile devices, each having at least one transmitter antenna configured to transmit radio-frequency (RF) signals and at least one receiver antenna configured to receive RF signals, first and second mobile devices of the plurality of mobile devices each sending a first wireless transmission of RF signals, the first mobile device receiving the first wireless transmission of RF signals sent by the second mobile device and sending a second wireless transmission of RF signals that conveys information about the first wireless transmission sent by the second mobile device; one or more base receivers, each base receiver having at least one receiver antenna configured to receive the wireless transmissions of RF signals transmitted by the first and second mobile devices of the plurality of mobile devices; and a base station in communication with each base receiver, the base station having a processor configured to calculate a position of the first mobile device of the plurality of mobile devices based on the first transmission of RF signals by the first mobile device, the processor being further configured to calculate a position of the second mobile device of the plurality mobile devices based on the first transmission of RF signals by the second mobile device, on the calculated position of the first mobile device, and on the second transmission of RF signals by the first mobile device that conveys timing information associated with the first transmission of RF signals sent by the second mobile device and received by the first mobile device.
 12. The position tracking system of claim 11, wherein each transmission of RF signals is an ultra-wideband transmission.
 13. The position tracking system of claim 11, wherein each transmitter antenna of the first mobile device uses a signal-transmission frequency that is different from a signal-reception frequency.
 14. The position tracking system of claim 11, wherein the processor of the base station is further configured to compute a location of each transmitter antenna of the first mobile device relative to each receiver antenna of the one or more base receivers.
 15. The position tracking system of claim 11, wherein the one or more base receivers includes one base receiver having at least three base receiver antennae.
 16. The position tracking system of claim 11, wherein the one or more base receivers includes at least three base receivers.
 17. The position tracking system of claim 11, wherein the base station computes orientation of the second mobile device.
 18. The position tracking system of claim 11, wherein the base station offsets the information associated with the first transmission of RF signals sent by the second mobile device by information associated with a distance of the first mobile device from the base station.
 19. A method of determining a position of a mobile radiofrequency (RF) signal transmitter, the method comprising the steps of: receiving a wireless transmission of RF signals from the mobile RF signal transmitter by receiver antennae of first and second stations; calculating, by each of the first and second stations, timing or phase difference data based on the wireless transmission of RF signals received from the mobile RF signal transmitter; transmitting, by the first station, a wireless transmission of RF signals that convey the timing or phase difference data calculated by the first station; receiving, by the second station, the wireless transmission of RF signals that convey the timing or phase difference data calculated by the first station; and calculating, by the second station, a position of the mobile RF-signal transmitter based on the timing or phase difference data calculated by the second station, the timing or phase difference data calculated by and received from the first station, and a relative position of the first station with respect to the second station when the first station received the wireless transmission of RF signals from the mobile RF signal transmitter. 